Communication control apparatus, communication system, and communication method

ABSTRACT

A communication control apparatus including: a processor configured to set each of starting time candidates for each of data communications performed by each of wireless communication apparatuses respectively, to estimate each of finishing time candidates for each of the data communications which corresponds to each of the starting time candidates, and to set each of starting times when each of wireless communication apparatuses is to start each of the data communications to each of the starting time candidates, by performing an optimization of a final finishing time candidate which is the final one of the finishing time candidates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2012-185436, filed on Aug. 24,2012, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a communication controlapparatus that controls data transmission to a plurality of wirelesscommunication apparatuses, a communication system, and a communicationmethod.

BACKGROUND

In this type of communication system, a mobile station apparatus mayfreely travel within a cell of a base station apparatus or among cells,so reception quality with which the mobile station apparatus receivessignals changes as the mobile station apparatus travels or a radiosignal environment changes with time. If the reception quality islowered, efficiency of data transmission to the mobile stationapparatus, for example, is lowered. This may cease communication withthe mobile station apparatus in some cases.

As a related technology, a data logging method is known that includesselection of one device from a plurality of devices and also includescalculation of a transfer period, including a starting time and afinishing time in log data transfer to a server, by using the transfersize of data to be transferred from the selected one device and atransfer period available to another device.

A known heterogeneous hybrid computer connecting system has a computerresource information manager that manages computing resourceinformation, in which information about dynamic performance includingthe traffic status of a network is included, and also has a jobscheduling manager that manages dynamic assignment of divided jobs to aplurality of computers according to the computing resource informationand a request.

A known communication terminal apparatus includes a first estimatedfinishing time calculator that calculates a estimated communicationfinishing time taken in a case in which data communication is placed ina wait state until a planned number of channels to be used are allprovided and the data communication is carried out by using the plannednumber of channels, a second estimated finishing time calculator thatcalculates a second estimated communication finishing time taken in acase in which if it is determined that a planned number of channels tobe used are not all provided, data communication is immediately startedby using only currently available channels, a selector that compares thetwo estimated communication finishing times and selects a communicationmode in which the estimated communication finishing time comes earlier,and a controller that provides control so that data communication iscarried out in the communication mode selected by the selector.

Japanese National Publication of International Patent Application No.2006-523984 and Japanese Laid-open Patent Publication Nos. 2005-56201and 6-205071 are examples of related art.

SUMMARY

According to an aspect of the invention, a communication controlapparatus including: a processor configured to set each of starting timecandidates for each of data communications performed by each of wirelesscommunication apparatuses respectively, to estimate each of finishingtime candidates for each of the data communications which corresponds toeach of the starting time candidates, and to set each of starting timeswhen each of wireless communication apparatuses is to start each of thedata communications to each of the starting time candidates, byperforming an optimization of a final finishing time candidate which isthe final one of the finishing time candidates.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of the structure of a communicationsystem;

FIG. 2 illustrates an example of the functional structure of a controlserver apparatus;

FIG. 3A illustrates an example of line information;

FIG. 3B illustrates an example of diagram information;

FIG. 3C illustrates an example of a quality database;

FIG. 3D illustrates reception quality estimated for a mobile stationapparatus;

FIG. 4 illustrates an example of the functional structure of a mobilestation apparatus;

FIG. 5 illustrates a first example of the operation of a control serverapparatus;

FIG. 6 illustrates an example of the operation of the mobile stationapparatus;

FIG. 7 illustrates a second example of the operation of the controlserver apparatus;

FIGS. 8A and 8B illustrate expected data rates at two mobile stationapparatuses;

FIGS. 9A and 9B illustrate an example of actual data rates at the twomobile station apparatuses;

FIGS. 10A and 10B illustrate another example of actual data rates at thetwo mobile station apparatuses;

FIGS. 11A and 11B illustrate another example of actual data rates at thetwo mobile station apparatuses;

FIG. 12 illustrates an example of the hardware structure of the controlserver apparatus; and

FIG. 13 illustrates an example of the hardware structure of the mobilestation apparatus.

DESCRIPTION OF EMBODIMENTS

In an example of a possible method of improving the efficiency of datatransmission to a wireless communication apparatus, future receptionquality at the wireless communication apparatus is estimated and datatransmission to the wireless communication apparatus is executed andstopped according to the estimation result. In this method, however, atransmission starting time is determined according to the estimationresult, so if a start of data transmission is delayed, a datatransmission completion time may be delayed.

If a plurality of wireless communication apparatuses that receive dataare present, data transmissions to these wireless communicationapparatuses may be concurrently carried out. Then, data transmissionoperation may become inappropriate. For example, there may be a case inwhich reception qualities at a plurality of wireless communicationapparatuses that receive data change similarly. This case may occurwhen, for example, a plurality of wireless communication apparatusesthat receive data travel together by using a public transportationsystem or the like.

If the reception quality of the wireless communication apparatusesbecomes good all at once, data transmission concentrates on the wirelesscommunication apparatuses, lowering data reception speeds at individualwireless communication apparatuses. When the reception qualities of thewireless communication apparatuses are lowered, data transmission stopsall at once, even if there are available wireless resources. Thus, thedata transmission completion time may be delayed.

An object of the apparatus or method disclosed in the present disclosureis to control data transmission with transmission completion times takeninto consideration when data items to be transmitted to a plurality ofwireless communication apparatuses are concurrently present.

1. First Embodiment 1.1 Example of the Structure of a CommunicationSystem

A preferred embodiment will be described below with reference to theattached drawings. FIG. 1 illustrates an example of the structure of acommunication system. The communication system 1 includes a controlserver apparatus 2, a gateway apparatus 3, base station apparatuses 4 aand 4 b, and mobile station apparatuses 5 a to 5 c.

The control server apparatus 2 controls transmission starting times atwhich content data is to be distributed from a content server apparatus101 to the mobile station apparatuses 5 a to 5 c. The content serverapparatus 101 is a content distribution server apparatus that providesservices through which website pages, news information, music, movingpictures, and other content data are distributed to the mobile stationapparatuses 5 a to 5 c through a network 100. The content serverapparatus 101 may be a server apparatus that supplies software andfirmware operating in the mobile station apparatuses 5 a to 5 c. Thecontrol server apparatus 2 and content server apparatus 101 areconnected to the gateway apparatus 3 through the network 100. Thecontrol server apparatus 2 is an example of a communication controlapparatus, and the mobile station apparatuses 5 a to 5 c are examples ofa wireless communication apparatus. The content data, software, andfirmware distributed from the content server apparatus 101 to the mobilestation apparatuses 5 a to 5 c are examples of data transmitted to acommunication control apparatus.

In the description that follows and on the attached drawings, thecontrol server apparatus, base station apparatus, mobile stationapparatus, gateway apparatus, and content server apparatus may bereferred to as the control server, base station, mobile station, GW, andcontent server, respectively. The base stations 4 a to 4 b may becollectively referred to as the base stations or base station 4. Themobile station apparatuses 5 a to 5 c may be collectively referred to asthe mobile stations or mobile station 5.

The GW 3 is a network apparatus that relays communication among thecontrol server 2, content server 101, and base stations 4. Each basestation 4 forms a cell by transmitting a radio signal and performs datatransmission and reception to and from a mobile station 5 located in thecell.

When the mobile station 5 is located in a cell formed by any one basestation 4, the mobile station 5 can perform signal transmission andreception to and from the control server 2 and content server 101through the base station 4. The mobile station 5 is a communicationapparatus that can travel at appropriate times; the mobile station 5 maybe, for example, a mobile telephone or a mobile information terminalapparatus. Although the base stations 4 a and 4 b and mobile stations 5a to 5 c are illustrated in FIG. 1, the communication system 1 mayinclude more base stations 4 and more mobile stations 5.

When determining a transmission starting time at which to transmitcontent data, the control server 2 predicts a moving route of the mobilestation 5 and estimates reception quality of a signal that the mobilestation 5 that will move along the predicted moving route will receivefrom the base station 4.

For example, the control server 2 estimates the moving route of themobile station 5 that travels by using a transportation system,according to operational information about the transportation system. Toreceive operational information used to predict the moving route of themobile station 5, the control server 2 may access an operationalinformation database 102, which retains operational information aboutthe transportation system, through the network 100, for example. In thedescription that follows and on the attached drawings, the database maybe referred to as the DB. The operational information DB 102 may beconnected to the control server 2 through a network different from thenetwork 100. Alternatively, the operational information DB 102 may bedisposed in the control server 2.

A quality DB 103 retains information about reception qualities ofsignals received from the base station 4 at positions in an areaincluding a cell of the base station 4. The control server 2 may accessthe quality DB 103 through the network 100 and may receive informationabout reception qualities at positions at which the mobile station 5traveling along the moving route will be present at future times. Thequality DB 103 may be connected to the control server 2 through anetwork different from the network 100. Alternatively, the quality DB103 may be disposed in the control server 2.

How the control server 2 predicts the moving route of the mobile station5, estimates reception quality, and controls a transmission time atwhich to transmit content data will be described in more detail.

1.2 Functional Structure

FIG. 2 illustrates an example of the functional structure of the controlserver 2. The control server 2 includes a start request receiver 10, amoving route predicting unit 11, a quality estimating unit 12, astarting time calculating unit 13, and a starting time transmitting unit14.

The start request receiver 10 receives a download start request signaltransmitted from the mobile station 5. The download start request signalis a signal through which the mobile station 5 requests the contentserver 101 to start to download content data. The download start requestsignal may include positional information about the current position ofthe mobile station 5, size information that specifies the file size ofthe content data to be downloaded, and base station information aboutthe base station 4 to which the mobile station 5 is being connected.

The moving route predicting unit 11 predicts the moving route of themobile station 5 according to the positional information about themobile station 5. An example of predicting a moving route according tothe operational information retained in the operational information DB102 will be described. The operational information DB 102 may include,for example, line information and diagram information as the operationalinformation. FIG. 3A illustrates an example of line information, andFIG. 3B illustrates an example of diagram information. The informationin FIGS. 3A and 3B are examples of operational information that isavailable when the transportation system is railroads.

The line information specifies coordinates at points on lines of thetransportation system. For example, the line information may include theinformation elements “line name”, “distance in kilometers”, “northlatitude”, and “east longitude”. The information element “line name”identifies a line of the transportation system. The information element“distance in kilometers” specifies a distance traveled from the originof the line to a point on the line along the line. The informationelements “north latitude” and “east longitude” specify a latitude andlongitude, respectively, as coordinate information at a point on theline. For example, the second row in FIG. 3A indicates that thecoordinates at a point 500 m apart from the origin of line A arelatitude 35.681614 degrees north and longitude 139.707831 degrees east.

The diagram information specifies operational schedules of individualtransportation apparatuses of the transportation system. For example,the diagram information may include the information elements “linename”, “train number”, “time”, and “distance in kilometers”. Theinformation element “line name” identifies a line of the transportationsystem. The information element “train number” identifies an individualtrain. The information elements “time” and “distance in kilometers”respectively indicate a time planned for the train during running and apoint at which the train is planned to be located at that time. Forexample, the second row in FIG. 3B indicates that the train with trainnumber 700H on line A is planned to be at a position 500 m apart fromthe origin at 13 hours, 00 minutes, 20 seconds.

Referring again to FIG. 2, the moving route predicting unit 11identifies a train that transports the mobile station 5 from, forexample, the positional information, current time, line information, anddiagram information provided for the mobile station 5. The moving routepredicting unit 11 predicts positional information about the mobilestation 5 at future times t1, t2, t3, and later from the diagraminformation and the coordinate information in the line information aboutthe identified train as a future moving route.

To predict the moving route of the mobile station 5, the moving routepredicting unit 11 may employ many methods other than the method inwhich operation information about the transportation system is used. Themoving route predicting unit 11 may retain behavior histories of theuser of the mobile station 5 and may predict a future moving route ofthe mobile station 5 from previous behavior histories. The moving routepredicting unit 11 may receive a travel destination from the mobilestation 5. The moving route predicting unit 11 may perform navigationprocessing in which a moving route from the current position of themobile station 5 to the travel destination is calculated.

The quality estimating unit 12 estimates the reception quality of asignal that the mobile station 5 will receive from the base station 4 atdifferent points on the moving route predicted by the moving routepredicting unit 11. When estimating the reception quality, the qualityestimating unit 12 references, for example, reception qualityinformation that is retained in the quality DB 103 according to theposition of the mobile station 5.

FIG. 3C illustrates an example of reception quality information retainedin the quality DB 103. The reception quality information indicatesreception qualities of signals received from base station 4 at positionsin an area including a cell of the base station 4. The reception qualityinformation may include the information elements “north latitude”, “eastlongitude”, and “reception quality”. The information elements “northlatitude” and “east longitude” is coordinate information that specifiesa position. The information element “reception quality” specifies thereception quality of a signal received from the base station 4 at thatposition. The reception quality may be specified in, for example,signal-to-interference power ratio (SIR) format, received signalstrength indication (RSSI) format, or a combination of these formats.For example, the second row in FIG. 3C indicates that reception SIR,which indicates reception quality, at a position with latitude 35.681614degrees north and longitude 139.707831 degrees east is 17 dB.

The reception quality information may be created by accumulatingreception qualities in a database together with measured positions, thereception qualities being measured by an operator who operates thecommunication system 1 and the mobile station 5 included in thecommunication system 1. Alternatively, the reception quality informationmay be calculated from the position of the base station 4, an antennaheight, an antenna angle, transmission power, and geographic informationin the cell.

The quality estimating unit 12 estimates the reception quality of themobile station 5 traveling along the moving route at a future time by,for example, taking a correspondence between the predicted moving routeof the mobile station 5 and the coordinate information in the quality DB103. FIG. 3D schematically illustrates reception quality estimated forthe mobile station 5. The quality estimating unit 12 estimates thereception quality of the mobile station 5 at future times t1, t2, t3,and later.

Referring again to FIG. 2, the starting time calculating unit 13calculates a download starting time at which to start to downloadcontent data to the mobile station 5 that has transmitted a downloadstart request signal. The starting time calculating unit 13 includes astarting time candidate specifying unit 15, a finishing time calculatingunit 16, and an optimization processing unit 17.

Of a plurality of mobile stations 5 that receive content data from thecontent server 101, the starting time candidate specifying unit 15identifies a set of mobile stations 5, (i=1, 2, . . . , Nu) at whichcontent data destined for the mobile stations 5 are combined in a commonwireless resource. The symbol Nu indicates a total number of mobilestations 5 _(i) included in this set. An example of a set of mobilestations 5 _(i) is a set of mobile stations 5 that are connected to thesame base station 4 and receive content data from the content server101. The starting time candidate specifying unit 15 may identify a setof mobile stations 5 _(i) according to, for example, base stationinformation, included in the download start request signal, about thebase station 4 to which the mobile station 5 is being connected. A setof mobile stations measured by the starting time candidate specifyingunit 15 will be referred to below as a plurality of mobile stations.

The starting time candidate specifying unit 15 specifies a plurality ofdownload starting time candidates for each of a plurality of mobilestations 5 _(i). The plurality of starting time candidates specified foreach of mobile stations 5 ₁, 5 ₂, . . . , 5 _(Nu) will be collectivelyreferred to as starting time candidates d₁, d₂, . . . , d_(Nu).

The starting time candidate specifying unit 15 specifies a plurality ofstarting time candidate combinations d̂(=d₁, d₂, . . . , d_(Nu))) bycombining a plurality of starting time candidates specified for each of5 ₁, 5 ₂, . . . , 5 _(Nu).

The finishing time calculating unit 16 calculates predicated throughputsθ₁(t) to θ_(Nu)(t) bps/Hz for the plurality of 5 ₁ to 5 _(Nu) at futuretime t according to the reception quality estimated by the qualityestimating unit 12 for the plurality of 5 ₁ to 5 _(Nu).

In a case in which mobile stations 5 ₁, 5 ₂, . . . , 5 _(Nu) start adownload at starting time candidates d₁ to d_(Nu) included in thestarting time candidate combinations d̂(=(d₁ to d_(Nu))), downloadfinishing times at the mobile stations 5 ₁, 5 ₂, . . . , 5 _(Nu) will bedenoted T₁(d̂) to T_(Nu)(d̂). Since the download finishing time depends onthe download starting time, finishing times T₁(d̂) to T_(Nu)(d̂) are eacha function of the starting time candidate combination d̂. The finishingtime calculating unit 16 calculates finishing times T₁(d̂) to T_(Nu)(d̂)for the specified plurality of starting time candidate combinations d̂.

The finishing times T₁(d̂) to T_(Nu)(d̂) satisfy equation (1) below.

B∫ _(d) _(i) ^(T) ^(i) ^((d̂))θ_(i)(t)/N(t)dt=S _(i)(i=1.2 . . . ,N_(u))  (1)

In equation (1), B indicates the system bandwidth of a wireless accessnetwork between the base station 4 and the mobile station 5, Si is thedownload size of remaining content data, and N(t) is a total number ofmobile stations 5 _(i) that are executing a download at time t, N(t)being given by equation (2) below.

$\begin{matrix}{{N(t)} = {\sum\limits_{i = 1}^{Nu}{{f\left( {t - d_{i}} \right)}{f\left( {{T_{i}\left( d^{\bigwedge} \right)} - t} \right)}}}} & (2)\end{matrix}$

The function f(x) is a step function, the value of which is 1 when x isgreater than or equal to 0, and 0 when x is smaller than 0.

Equation (1) is used when wireless resources are evenly assigned tomobile stations 5 _(i). In an embodiment in which different amount ofwireless resources are assigned to different mobile stations 5 _(i), theleft side of equation (1) may be multiplied by a coefficient suitable tothese differences.

When equations (1) and (2) are quantized by a discrete time (one secondinterval in these equations), they are rewritten as equations (3) and(4) below.

$\begin{matrix}{{B{\sum\limits_{n = d_{i}}^{{T_{i}{(d^{\bigwedge})}} - 1}{{\theta_{i}(n)}/{N(n)}}}} = {S_{i}\left( {{i = 1},{2\mspace{14mu} \ldots}\mspace{14mu},N_{u}} \right)}} & (3) \\{{N(n)} = {\sum\limits_{i = 1}^{Nu}{{f\left( {n - d_{i}} \right)}{f\left( {{T_{i}\left( d^{\bigwedge} \right)} - 1 - n} \right)}}}} & (4)\end{matrix}$

With time discretely advancing, the finishing time calculating unit 16determines whether a download at mobile stations 5 ₁ to 5 _(Nu) has beenfinished according to equations (3) and (4) to calculate finishing timesT₁(d̂) to T_(Nu)(d̂).

The optimization processing unit 17 solves an optimization problem,determined according to a desired download method, of an objectivefunction of finishing time T_(i)(d̂) calculated by the finishing timecalculating unit 16 to determine download starting time d₁ at which tostart a download at mobile station 5 _(i). To comprehensively move updownload finishing times T_(i)(d̂) at all mobile stations 5 _(i), forexample, it suffices to select the starting time candidate combination d̂by which an objective function C (d̂) represented by equation (5) belowis minimized as download starting time d_(i) at each mobile stations 5_(i).

$\begin{matrix}{{C\left( d^{\bigwedge} \right)} = {\sum\limits_{i = 1}^{N_{u}}{T_{i}\left( d^{\bigwedge} \right)}}} & (5)\end{matrix}$

The objective function C (d̂) in equation (5) represents the sum ofdownload finishing times T_(i)(d̂) at all mobile stations 5 _(i). Thatis, the objective function C (d̂) in equation (5) represents the sum oftimes each of which is a time from a certain reference time of day totime T_(i)(d̂) at which a download is finished at each of all mobilestations 5 _(i).

The starting time transmitting unit 14 transmits download starting timed_(i), at each mobile stations 5 _(i), determined by the optimizationprocessing unit 17 to relevant mobile stations 5 _(i).

Next, the functions of the mobile station 5 will be described. FIG. 4illustrates an example of the functional structure of the mobile station5. The mobile station 5 includes a receiver 20, a transmitter 21, amanipulation accepting unit 22, a content controller 23, a positionalinformation obtaining unit 24, a content retaining unit 25, and contentoutput unit 26.

The receiver 20 receives an outbound link signal transmitted from thebase station 4 through an antenna, after which the receiver 20demodulates and decodes the outbound link signal. The outbound linksignal includes content data transmitted from the content server 101through the base station 4 and also includes information that specifiesa time at which to start to download the content data, the informationbeing transmitted from control server 2 through the base station 4. Thereceiver 20 outputs the received content data to the content retainingunit 25 and also outputs the information about the download startingtime to the content controller 23.

The transmitter 21 encodes and modulates an inbound link signal andsends the modulated signal to the base station 4 through the antenna.The inbound link signal includes a download start request signal that istransmitted to the control server 2 through the base station 4. Theinbound link signal also includes a download request signal that istransmitted to the content server 101 through the base station 4. Thedownload request signal is a signal through which the mobile station 5requests the content server 101 to transmit content data. Upon receiptof the download request signal, the content server 101 starts totransmit content data. The transmitter 21 receives the download startrequest signal and download request signal from the content controller23 and transmits the download start request signal and download requestsignal to the control server 2 and content server 101, respectively, asinbound signals.

The manipulation accepting unit 22 accepts a command manipulationperformed by the user for the mobile station 5. The manipulationaccepting unit 22 may be, for example, a keyboard, buttons, a touchpanel, a microphone, or another information input device attached to themobile station 5. The content controller 23 creates a download startrequest signal, which is used to receive content data, in response to acommand entered by the user through the manipulation accepting unit 22,and outputs the created signal to the transmitter 21. As describedabove, the download start request signal includes positional informationthat specifies the current position of the mobile station 5, sizeinformation that specifies the file size of content data to bedownloaded, and base station information about the base station 4 towhich the mobile station 5 is being connected.

The content controller 23 receives positional information about themobile station 5, which is transmitted as a download start requestsignal, from the positional information obtaining unit 24. Thepositional information obtaining unit 24 obtains the current position ofthe mobile station 5 and outputs positional information indicting thecurrent position to the content controller 23. An example of thepositional information obtaining unit 24 may be a Global PositioningSystem (GPS) device or an inertial navigation device.

When the content controller 23 receives, from the control server 2,starting time information that specifies a time at which to start todownload content data, the content controller 23 monitors the arrival ofthe download starting time specified in the starting time information.When the download starting time comes, the content controller 23 outputsa download request signal to the transmitter 21.

Upon receipt of the download request signal, the transmitter 21 sends itto the content server 101. The content server 101 starts to transmitcontent data to the receiver 20 in response to the received downloadrequest signal. The content data received by the receiver 20 is storedin the content retaining unit 25. The content retaining unit 25 may havea hard disk drive, a memory, or another information storage device toretain content data.

The content output unit 26 outputs content data to be stored in thecontent retaining unit 25 in response to a command entered by the userthrough the manipulation accepting unit 22. The content output unit 26may have a display device on which visual content data, for example, isdisplayed. The content output unit 26 may have a speaker or anotheraudio signal device from which, for example, acoustic content data isoutput.

1.3 Explanation of Operation

Next, the operations of the control server 2 and mobile station 5 willbe described. FIG. 5 illustrates a first example of the operation of thecontrol server 2.

In operation AA, the start request receiver 10 receives download startrequest signals from a plurality of mobile stations 5 _(i). In operationAB, the moving route predicting unit 11 predicts the moving routes ofthe plurality of mobile stations 5 _(i) from positional informationabout the plurality of mobile stations 5 _(i). In operation AC, thequality estimating unit 12 estimates reception qualities of signals thatthe plurality of mobile stations 5 _(i) will receive from their relevantbase stations 4 at future times.

In operation AD, the starting time candidate specifying unit 15specifies a plurality of download starting time candidates for each ofthe plurality of mobile stations 5 _(i). The starting time candidatespecifying unit 15 combines the plurality of starting time candidatesspecified for each of the plurality of mobile stations 5 ₁, 5 ₂, . . . ,5 _(Nu) and specifies a plurality of starting time candidatecombinations d̂(=(d₁, d₂, . . . , d_(Nu))).

In operation AE, the finishing time calculating unit 16 calculatesfinishing times T₁(d̂) to T_(Nu)(d̂) for each of the specified pluralityof starting time candidate combinations d̂. In operation AF, theoptimization processing unit 17 determines starting time d₁ at whicheach mobile station 5 _(i) starts a download by solving the optimizationproblem of the objective function of finishing time T₁(d̂). In operationAG, the starting time transmitting unit 14 transmits, to each mobilestation 5 _(i), starting time d₁, determined by the optimizationprocessing unit 17, at which each mobile station 5 _(i) starts adownload.

Next, an example of the operation of the mobile station 5 will bedescribed with reference to FIG. 6. In operation BA, the contentcontroller 23 decides whether a command to download content data hasbeen entered by the user from the manipulation accepting unit 22. If adownload command has been entered (the result in operation BA is Yes),the operation proceeds to operation BB. If a download command has notbeen entered (the result in operation BA is No), the operation returnsto operation BA.

In operation BB, the content controller 23 creates a download startrequest signal and outputs it to the transmitter 21. The transmitter 21receives the download start request signal and transmits it to thecontrol server 2 through the base station 4 and GW 3.

In operation BC, the content controller 23 receives, from the controlserver 2, starting time information that specifies a time at which tostart to download content data. In operation BD, the content controller23 decides whether the download starting time specified in the startingtime information has come. If the download starting time has arrived(the result in operation BD is Yes), the operation proceeds to operationBE. If the download starting time has not come (the result in operationBD is No), the operation returns to operation BD.

In operation BE, the content controller 23 transmits a download requestsignal to the transmitter 21. The transmitter 21 receives the downloadrequest signal and outputs it to the content server 101 through the basestation 4 and GW 3. In operation BF, the receiver 20 receives contentdata from the content server 101. The content data received by thereceiver 20 is stored in the content retaining unit 25.

In operation BG, the content controller 23 decides whether a command toreproduce content data has been entered by the user from themanipulation accepting unit 22. If a reproduction command has beenentered (the result in operation BG is Yes), the operation proceeds tooperation BH. If a reproduction command has not been entered (the resultin operation BG is No), the operation returns to operation BG. Inoperation BH, the content controller 23 causes the content output unit26 to output content data to be stored in the content retaining unit 25.

1.4 Advantageous Effects

In this embodiment, a download starting time is determined by solvingthe optimization problem of the objective function of a downloadfinishing time at the mobile station 5. Accordingly, it is possible tooptimize a download operation in consideration of a download finishingtime. With equation (5) above, a download operation is controlled sothat a download is finished at the mobile station 5 at the earliesttime.

In this embodiment, a download starting time is determined by solvingthe optimization problems of the objective functions of downloadfinishing times T₁(d̂) to T_(Nu)(d̂) at a plurality of mobile stations 5 ₁to 5 _(Nu). Accordingly, it is possible to optimize a download operationin consideration of concurrent downloads among the plurality of mobilestations 5 ₁ to 5 _(Nu). With equation (5) above, a download operationis controlled so that all download finishing times T_(i)(d̂) at theplurality of mobile stations 5 ₁ to 5 _(Nu) come comprehensively early.

1.5 Variation

As the objective function of download finishing time T_(i)(d̂) used todetermine download starting time d_(i), various functions can be usedaccording to a desired download method. To improve download efficiencyby minimizing the amount of wireless resources used for a download, forexample, it suffices to select the starting time candidate combination d̂that minimizes the objective function C (d̂) represented by equation (6)as download starting time d_(i).

$\begin{matrix}{{C\left( d^{\bigwedge} \right)} = {\sum\limits_{i = 1}^{N_{u}}{D_{i}\left( d^{\bigwedge} \right)}}} & (6)\end{matrix}$

D_(i)(d̂) (=T_(i)(d̂)−d_(i)) represents a period from a download startingtime to a download finishing time, that is, a download execution time,and the objective function C(d̂) in equation (6) indicates the sum ofdownload execution times taken at all mobile stations 5 _(i).Accordingly, when the objective function C(d̂) in equation (6) isminimized, the sum of download execution times taken at all mobilestations 5 _(i) is minimized, so the amount of wireless resources to beused is minimized.

To optimize the starting time so that download times at a plurality ofmobile stations 5 _(i) do not exceed their allowable finishing timeT_(max, i), the starting time candidate combination d̂ that minimizes theobjective function C(d̂) in equation (7) may be selected as downloadstarting time d_(i).

$\begin{matrix}{{C\left( d^{\bigwedge} \right)} = {\sum\limits_{i = 1}^{N_{u}}{g\left( {{T_{i}\left( d^{\bigwedge} \right)} - T_{\max,i}} \right)}}} & (7)\end{matrix}$

The function g(x) may be a function that takes 0 when x is smaller thanor equal to 0 and is a monotone increasing function of x when x isgreater than 0. For example, the function g(x) may be a ramp functionthat takes 0 when x is smaller than or equal to 0 and takes x when x isgreater than 0. The objective function C(d̂) in equation (7) represents aproduct obtained by multiplying a difference by the functiong(T_(i)(d̂)−T_(max, i)) for each of all mobile stations 5 i, thedifference being obtained by subtracting threshold T_(max, i) fromdownload finishing times T_(i)(d̂).

When the objective function C(d̂) in equation (7) is minimized, ifdownload finishing times T_(i)(d̂) at all mobile station 5 _(i) aresmaller than or equal to allowable finishing time T_(max, i), they areminimized to 0. Accordingly, download starting time d_(i) is optimizedso that the download finishing time at each of a plurality of mobilestations 5 _(i) does not exceed the relevant allowable finishing timeT_(max, i).

Although, in this embodiment, the control server 2 and content server101 are different server apparatuses, this is not a limitation; thecontrol server 2 and content server 101 may be a single server apparatusin another embodiment.

2. Second Embodiment 2.1 Explanation of Operation

Next, another embodiment of the communication system 1 will bedescribed. It is now assumed that after the optimization processing unit17 had already determined download starting times d₁ to d_(Nu) at mobilestations 5 ₁ to 5 _(Nu), new mobile station 5 _(Nu+1) has transmitted adownload start request signal. In this description, a mobile station forwhich download starting time d₁ has already been determined is referredto as a mobile station in the downloading state.

In a certain embodiment, download starting times d₁ to d_(Nu) at mobilestations 5 ₁ to 5 _(Nu) may be recalculated together with downloadstarting time d_(Nu+1) at new mobile station 5 _(Nu+1) by thedetermination method described above in the first embodiment. In thiscase, a mobile station, of mobile stations 5 ₁ to 5 _(Nu) in thedownloading state, at which a download is actually being carried out maysuspend the download and then may restart the download at a startingtime that is newly determined after the suspension.

In the second embodiment, only download starting time d_(Nu+1) at newmobile station 5 _(Nu+1) is optimized without changing download startingtimes d₁ to d_(Nu) at mobile stations 5 ₁ to 5 _(Nu) in the downloadingstate.

The starting time candidate specifying unit 15 specifies a plurality ofdownload starting time candidates d_(Nu+1) at new mobile station 5_(Nu+1). Since the download finishing times at mobile stations 5 ₁ to 5_(Nu), 5 _(Nu+1) change depending on the download starting time at newmobile station 5 _(Nu+1), the finishing time is a function of startingtime candidate d_(Nu+1). The download finishing times at mobile stations5 ₁ to 5 _(Nu), 5 _(Nu+1) will be denoted T₁(d_(Nu+1)) toT_(Nu)(d_(Nu+1)), T_(Nu+1)(d_(Nu+1)), respectively.

With time discretely advancing, the finishing time calculating unit 16determines whether a download at mobile stations 5 ₁ to 5 _(Nu), 5_(Nu+1) has been finished according to equations (8) and (9) tocalculate finishing times T₁(d_(Nu+1)) to T_(Nu)(d_(Nu+1)),T_(Nu+1)(d_(Nu+1)).

$\begin{matrix}{{B{\sum\limits_{n = d_{i}}^{{T_{i}{(d_{{Nu} + 1})}} - 1}{{\theta_{i}(n)}/{N(n)}}}} = {S_{i}\left( {{i = 1},{2\mspace{14mu} \ldots}\mspace{14mu},{N_{u} + 1}} \right)}} & (8) \\{{N(n)} = {\sum\limits_{i = 1}^{{Nu} + 1}{{f\left( {n - d_{i}} \right)}{f\left( {{T_{i}\left( d_{{Nu} + 1} \right)} - 1 - n} \right)}}}} & (9)\end{matrix}$

The optimization processing unit 17 determines download starting timed_(NU+1) at new mobile station 5 _(Nu+1) by solving the optimizationproblem of the objective function of finishing time T₁(d_(Nu+1)). Forexample, the optimization processing unit 17 may select starting timecandidate d_(NU+1) by which the objective function C(d_(Nu+1)) inequation (10) below is minimized as download starting time d_(Nu+1) atnew mobile station 5 _(Nu+1). As in equation (5) above, the objectivefunction C(d_(Nu+1)) in equation (10) below represents the sum ofdownload finishing times at all mobile stations 5 ₁ to 5 _(Nu), 5_(Nu+1). An objective function as in equations (6) and (7) above may beused in the second embodiment.

$\begin{matrix}{{C\left( d_{{Nu} + 1} \right)} = {\sum\limits_{i = 1}^{N_{u} + 1}{T_{i}\left( d_{{Nu} + 1} \right)}}} & (10)\end{matrix}$

The operation of the control server 2 in the second embodiment will bedescribed with reference to FIG. 7. It is assumed here that downloadstarting times d₁ to d_(NU) at mobile stations 5 ₁ to 5 _(Nu) have beendetermined before operation CA described below is executed.

In operation CA, the start request receiver 10 receives a download startrequest signal from new mobile station 5 _(Nu+1). In operation CB, themoving route predicting unit 11 predicts the moving routes of aplurality of mobile stations 5 ₁ to 5 _(Nu+1). In operation CC, thequality estimating unit 12 estimates reception qualities of signals thatthe plurality of mobile stations 5 ₁ to 5 _(Nu+1) will receive fromtheir relevant base stations 4 at future times. The reception quality atmobile stations 5 ₁ to 5 _(Nu), which had been estimated when downloadstarting times d₁ to d_(NU) at mobile stations 5 ₁ to 5 _(Nu) had beendetermined before operation CA as been executed, may be stored in, forexample, the quality estimating unit 12. If the reception qualities atmobile stations 5 ₁ to 5 _(Nu), which had been estimated beforeoperation CA has been executed, can be used, the predicting of themotion paths of mobile stations 5 ₁ to 5 _(Nu) and the estimation ofreception qualities at mobile stations 5 ₁ to 5 _(Nu) may be omitted inoperations CB and CC.

In operation CD, the starting time candidate specifying unit 15specifies a plurality of download starting time candidates d_(NU+1) fornew mobile station 5 _(Nu+1). In operation CE, the finishing timecalculating unit 16 calculates finishing times T₁(d_(Nu+1)) toT_(Nu+1)(d_(Nu+1)) for each of the specified plurality of starting timecandidates d_(Nu+1).

In operation CF, the optimization processing unit 17 determines startingtime d_(NU+1) at which new mobile station 5 _(Nu+1) starts a download bysolving the optimization problem of the objective function of finishingtime T₁(d_(Nu+1)). In operation CG, the starting time transmitting unit14 transmits download starting time d_(Nu+1) determined by theoptimization processing unit 17 to new mobile station 5 _(Nu+1).

2.2 Example of Operation

Next, an example of an operation state when a download is controlledaccording to the second embodiment will be described by making acomparison with a case in which download starting times are notcontrolled and a case in which download starting times are controlled inanother method. It is assumed here that two mobile stations 5 a and 5 b,which are connected to the same base station 4, start to downloadcontent data.

FIGS. 8A and 8B illustrate expected data rates at the mobile stations 5a and 5 b. The expected data rates in FIGS. 8A and 8B are represented asa value relative to the amount of data that can be transmitted in a timeinterval T. The expected data rates at the mobile station 5 a in aperiod from times 0 to T, in a period from times T to 2T, in a periodfrom times 2T to 3T, in a period from times 3T to 4T, in a period fromtimes 4T to 5T, in a period from times 5T to 6T, and in a period fromtimes 6T to 7T are 4, 4, 4, 2, 2, 2, and 1, respectively.

The expected data rates at the mobile station 5 b in a period from times0 to T, in a period from times T to 2T, in a period from times 2T to 3T,in a period from times 3T to 4T, in a period from times 4T to 5T, in aperiod from times 5T to 6T, and in a period from times 6T to 7T are 2,1, 8, 6, 4, 1, and 1, respectively. If wireless packets are transmittedat intervals of about 1 ms, the time interval T may be longer than thewireless packet transmission interval; for example, the time interval Tmay be on the order from one second to several minutes.

Download finishing times at the mobile stations 5 a and 5 b will becompared, assuming that a value relative to the amount of datadownloaded at the mobile station 5 a is 12 and a value relative to theamount of data downloaded at the mobile station 5 b is 10 and that themobile station 5 a generates a content data download request at time 0and mobile station 5 b generates it at time T.

2.2.1 Case in which Download Starting Times are Not Controlled

FIGS. 9A and 9B illustrate an example of actual data rates at the mobilestations 5 a and 5 b in a case in which download starting times are notcontrolled. When download starting times are not controlled, the mobilestations 5 a and 5 b start a download at times 0 and T, respectively.

In a period from times 0 to T and a period from times 6T to 7T, duringwhich only the mobile station 5 a is executing a download, the datarates at the mobile station 5 a are the same as the expected data rates4 and 1. In periods during which both the mobile stations 5 a and 5 bare executing a download, if wireless resources are assumed to be evenlydivided between the mobile stations 5 a and 5 b, the actual data ratebecomes half of the expected data rate. Accordingly, in a period fromtimes T to 2T, in a period from times 2T to 3T, in a period from times3T to 4T, in a period from times 4T to 5T, and in a period from times 5Tto 6T, during which the mobile stations 5 a and 5 b concurrentlyexecutes a download, the data rate at the mobile station 5 a becomeshalf of the expected data rate. Specifically, the data rates at themobile station 5 a in a period from times T to 2T, in a period fromtimes 2T to 3T, in a period from times 3T to 4T, in a period from times4T to 5T, and in a period from times 5T to 6T becomes 2, 2, 1, 1, and 1,respectively.

Similarly, the data rates at the mobile station 5 b in a period fromtimes T to 2T, in a period from times 2T to 3T, in a period from times3T to 4T, in a period from times 4T to 5T, and in a period from times 5Tto 6T becomes 0.5, 4, 3, 2 and 0.5, respectively. As a result, a time atwhich the mobile station 5 a completes the downloading of content databy a data amount of 12 is 7T. A period during which the mobile station 5a continues downloading is 7T. By contrast, a time at which the mobilestation 5 b completes the downloading of content data by a data amountof 10 is 6T. A period during which the mobile station 5 b continuesdownloading is 5T.

2.2.2 Case in which the Download Starting Time is IndependentlyControlled for Each Mobile Station

Next, it will be assumed that download starting times at the mobilestations 5 a and 5 b are individually controlled. FIGS. 10A and 10Billustrate an example of actual data rates at the mobile stations 5 aand 5 b when download starting times at the mobile stations 5 a and 5 bare individually controlled.

In this example, the download starting time is controlled so that adownload is started in a period in which the expected data rate at themobile station is maximized. Therefore, a download at the mobile station5 a is started at time 0 and a download at the mobile station 5 b isstarted at time 2T. As a result, the download at the mobile station 5 ais finished at time 5T, and a period during which the mobile station 5 acontinues downloading is 5T. By contrast, the download at the mobilestation 5 b is finished at time 6T, and a period during which the mobilestation 5 b continues downloading is 4T.

In comparison with the case in which the download starting time is notcontrolled, the download finishing time and the download period at themobile station 5 a have been improved from 7T to 5T. However, thedownload finishing time at the mobile station 5 b has not been improved;that time stays at 6T.

2.2.3 Case in which Download Starting Times are Controlled According tothe Second Embodiment

FIGS. 11A and 11B illustrate an example of actual data rates at themobile stations 5 a and 5 b in a case in which download starting timesare controlled according to the second embodiment. In this example,equation (10) above is used as an objective function to control thedownload starting times so that the sum of the times at which a downloadis finished at the mobile stations 5 a and 5 b is minimized.

In this example, when a download at the mobile station 5 a is started attime 0 and a download at the mobile station 5 b is started at time 3T,the sum of the download finishing times at the mobile stations 5 a and 5b is minimized. As a result, the download at the mobile station 5 a isfinished at time 3T, and a period during which the mobile station 5 acontinues downloading is 3T. By contrast, the download at the mobilestation 5 b is finished at time 5T, and a period during which the mobilestation 5 b continues downloading is 2T.

In comparison with the case in which the download starting time is notcontrolled, the download finishing time at the mobile station 5 a hasbeen improved from 7T to 3T, and the download finishing time at themobile station 5 b has been improved from 6T to 5T. In comparison withthe case in which the download starting time is independently controlledfor each mobile station, the download finishing time at the mobilestation 5 a has been improved from 5T to 3T, and the download finishingtime at the mobile station 5 b has been improved from 6T to 5T. It isalso found that the download periods have been also improved.

2.3 Advantageous Effects

When a download occurs at new mobile station 5 _(Nu+1), only thedownload starting time at new mobile station 5 _(Nu+1) is optimized, sothe amount of calculation can be reduced when compared with a case inwhich download starting times d₁ to d_(Nu) at mobile stations 5 ₁ to 5_(Nu) are also recalculated.

In addition, there is no requirement to temporarily suspend a downloadthat has been already started to recalculate download starting times d₁to d_(Nu) at mobile stations 5 ₁ to 5 _(Nu) in the downloading state,suppressing the wireless resource usage efficiency from being lowered.

3. Hardware Structure

Finally, an example of the structure of hardware that implements thecontrol server 2 and mobile station 5 described above will be described.FIG. 12 illustrates an example of the hardware structure of the controlserver 2. The control server 2 includes a central processing unit (CPU)50, a memory 51, and a network interface circuit 52. In FIG. 12, theterm network interface is represented as NIF. The memory 51 may includea non-volatile memory, a read-only memory (ROM), a random-access memory(RAM), and other memories that store computer programs and data.

The operations, described above, of the start request receiver 10 andstarting time transmitting unit 14 included in the control server 2illustrated in FIG. 2 are executed when the CPU 50 and NIF circuit 52cooperate. The operations, described above, of the moving routepredicting unit 11, quality estimating unit 12, and starting timecalculating unit 13 are executed by the CPU 50.

FIG. 13 illustrates an example of the hardware structure of the mobilestation 5. The mobile station 5 includes a CPU 60, a memory 61, alarge-scale integrated (LSI) circuit 62, wireless communication circuits63 and 64, an input unit 65, an output unit 66, and a positioning unit67. The memory 61 may include a non-volatile memory, a ROM, and a RAM.The LSI circuit 62 may include a field-programmable gate array (FPGA),an application-specific integrated circuit (ASIC), and a digital signalprocessor (DSP).

The wireless communication circuit 63 may include an analog-to-digitalconverting circuit and a frequency converting circuit. The communicationcircuit 64 may include a digital-to-analog converting circuit and afrequency converting circuit. The input unit 65 may include a keyboard,buttons, a touch panel, a microphone, and other information inputdevices. The output unit 66 may include a display unit and an audiosignal device. The positioning unit 67 may include a GPS device thatmeasures the current position of the mobile station 5 and an inertialnavigation device.

The operations, described above, of the receiver 20 and transmitter 21included in the mobile station 5 illustrated in FIG. 4 are executed bythe wireless communication circuits 63 and 64. The operations, describedabove, of the manipulation accepting unit 22 and content output unit 26are executed by the input unit 65 and output unit 66, respectively. Theoperation, described above, of the content controller 23 is executed bythe CPU 60. The operation, described above, of the positionalinformation obtaining unit 24 is executed by the positioning unit 67.Data to be retained in the content retaining unit 25 is stored in thememory 61.

The hardware structures illustrated in FIGS. 12 and 13 are only examplesused to describe an embodiment. The control server 2 and mobile station5 described in this description may use any other hardware structures ifthey execute operations described below.

The functional structures illustrated in FIGS. 2 and 4 are drawn,centered around the functions of the control server 2 and mobile station5 described in this description. The control server 2 and mobile station5 may include any structural elements other than the structural elementsin FIGS. 2 and 4.

Series of operations described with reference to FIGS. 5 to 7 may beinterpreted as methods including a plurality of steps. In this case, anoperation may be read as referring to a step.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A communication control apparatus comprising: aprocessor configured to set each of starting time candidates for each ofdata communications performed by each of wireless communicationapparatuses respectively, to estimate each of finishing time candidatesfor each of the data communications which corresponds to each of thestarting time candidates, and to set each of starting times when each ofwireless communication apparatuses is to start each of the datacommunications to each of the starting time candidates, by performing anoptimization of a final finishing time candidate which is the final oneof the finishing time candidates.
 2. The communication control apparatusaccording to the claim 1, wherein the processor is further configured toestimate each of channel qualities between a base station and each ofthe wireless communication apparatuses respectively, and the processorsets each of the starting times based on each of the channel qualities.3. The communication control apparatus according to the claim 2, whereinthe processor is further configured to presume each of moving routes ofeach of the wireless communication apparatuses, and the processorestimates each of the channel qualities based on each of the movingroutes.
 4. The communication control apparatus according to the claim 1,wherein the processor performs the optimization by using an objectivefunction for an optimization problem, and the objective function is asum of the finishing time candidates.
 5. The communication controlapparatus according to the claim 1, wherein the processor performs theoptimization by using an objective function for an optimization problem,the objective function is a sum of communication periods, and each ofthe communication periods is a period between the starting timecandidates and each of the finishing time candidates respectively. 6.The communication control apparatus according to the claim 1, whereinthe processor performs the optimization by using an objective functionfor an optimization problem, and the objective function is a product ofelement functions, and each of element functions is 0 when each ofdifferences between each of the finishing time candidates and aspecified threshold value is equal to or less than 0, and is a monotoneincreasing function when each of the differences is more than
 0. 7. Thecommunication control apparatus according to the claim 1, wherein theprocessor is further configured to, after starting at least one of thecommunications in accordance with the starting time, set a next startingtime candidate for a next data communication performed by a nextwireless communication apparatus, to estimate a next finishing timecandidates for the next data communication which corresponds to the nextstarting time candidate, and to set a next starting time when the nextwireless communication apparatus is to start the next data communicationto the next starting time candidate, by performing an optimization ofthe next finishing time candidates.
 8. A communication control systemcomprising: wireless communication apparatuses; and a communicationcontrol apparatus including a processor configured to set each ofstarting time candidates for each of data communications performed byeach of the wireless communication apparatuses respectively, to estimateeach of finishing time candidates for each of the data communicationswhich corresponds to each of the starting time candidates, and to seteach of starting times when each of wireless communication apparatusesis to start each of the data communications to each of the starting timecandidates, by performing an optimization of a final finishing timecandidate which is the final one of the finishing time candidates.
 9. Acommunication control method comprising: setting each of starting timecandidates for each of data communications performed by each of wirelesscommunication apparatuses respectively; estimating each of finishingtime candidates for each of the data communications which corresponds toeach of the starting time candidates; and setting each of starting timeswhen each of wireless communication apparatuses is to start each of thedata communications to each of the starting time candidates, byperforming an optimization of a final finishing time candidate which isthe final one of the finishing time candidates.